Label with a diffractive bar code and reading arrangement for such labels

ABSTRACT

A label ( 1 ) made from a layer composite ( 15 ) includes at least one machine-readable diffractive bar code ( 3 ) consisting of narrow rectangular fields ( 4 ) occupied by the optically active structures and intermediate surfaces ( 5 ). The optically active structures which are covered by a reflection layer are embedded between layers of the layer composite ( 15 ). The diffractive relief structure used in the diffractive bar code ( 3 ) for the fields ( 4 ) diffracts and polarizes incident light and scatters the diffracted light into a half-space above the diffractive relief structure. A second diffractive relief structure differs at least in respect of the polarization of the polarizedly backscattered light with respect to the first diffractive relief structure. The second diffractive relief structure can be used for example for field surfaces of a second bar code in the bar code field ( 9 ) on the label ( 1 ) or for the intermediate surfaces ( 5 ). The light which is polarizedly backscattered at the diffractive bar code ( 3 ) can be detected by means of one of the known commercially available reading apparatuses for bar codes produced by printing. The bar code produced by printing can be used for individualizing the labels ( 1 ).

This application claims priority based on an International Applicationfiled under the Patent Cooperation Treaty, PCT/EP02/09985, filed on Sep.6, 2002, and German Patent Application No. 101 46 508.4, filed on Sep.21, 2001, both of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The invention relates to a label with a diffractive bar code as setforth in the classifying portion of claim 1 and a reading arrangementfor recognizing information on such labels as set forth in theclassifying portion of claim 13.

Such labels are used for identifying articles, identity cards or passesor stock bonds and bear numerical information relating to the article,the identity card or the bond. The bar code of such labels is read offby optical means and is distinguished by good machine readability of theinformation contained in the bar code.

Various kinds of bar code are known, such as for example in accordancewith MIL-STD-1189 or in accordance with the “European Article NumberingCode”, in which an item of information is contained in the arrangementof bar elements and intermediate spaces, of various widths. The barelements are applied in a color contrasting with the intermediatespaces, to a carrier, usually paper, by means of a simple printingprocess. Reading apparatuses which can read off such bar codes arecommercially available.

In accordance with U.S. Pat. No. 5,900,954 the level of safeguard of thebar code against forgery can be increased by the bar code being printedonto a carrier with a hologram. The bar code extends entirely or atleast partially over the hologram.

EP 0 366 858 A1 describes various configurations of diffractive barcodes which, instead of printed bar elements, have surface elements withdiffraction gratings. In comparison with the bar codes produced by aprinting process the diffractive bar codes have a high level ofsafeguard against forgery. It will be noted however that the advantageof the high anti-forgery safeguard is achieved at the expense of atolerance, which is low in comparison with the bar codes produced by aprinting process, in regard to orientation of the diffractive bar codewith respect to the reading beam of the reading arrangement, and alimitation in terms of the distance between the reading apparatus andthe label, to a few centimeters. In addition the bar code which isproduced individually by a printing process, with individualinformation, is extremely inexpensive while the diffractive bar codescan rationally be produced at viable costs, only in large quantitieswith identical information.

Surfaces arranged in a mosaic-like configuration, with microscopicallyfine diffraction structures which are embossed into plastic material,are known for example from EP-0 105 099 B1 and EP 375 833 B1. Designconfigurations of security labels with structures having an opticaldiffraction effect and the materials which can be used for that purposeare summarized in U.S. Pat. No. 4,856,857.

DE-OS No 1 957 475 and CH 653 782 disclose a further family ofmicroscopically fine relief structures having an optical diffractioneffect, under the name kinoform. It is only when the kinoform isilluminated with substantially coherent light that the light isdeflected by the kinoform asymmetrically into a single spatial anglewhich is predetermined by the relief structure of the kinoform.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an inexpensive,optically machine-readable label having at least one diffractive barcode which can be read from a distance of several decimeters withcommercially available reading apparatuses.

According to the invention that object is attained by the featuresrecited in the characterizing portion of claim 1. Advantageousconfigurations of the invention are set forth in the appendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in greater detail hereinafterand illustrated in the drawing in which:

FIG. 1 shows a label with a diffractive bar code,

FIG. 2 shows a cross-section through the label,

FIG. 3 shows a portion from FIG. 2 on an enlarged scale,

FIG. 4 shows a graph,

FIG. 5 shows the diffractive bar code,

FIG. 6 shows two parallel bar codes,

FIGS. 7 a and 7 b show nested bar codes,

FIG. 8 shows a first reading arrangement, and

FIG. 9 shows a second reading arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 reference 1 denotes a label, reference 2 denotes an area witha diffractive bar code 3, 4 denotes fields and 5 denotes intermediatesurfaces of the bar code 3. The fields 4 and the intermediate surfaces 5are rectangular bars which are arranged with their longitudinal sidestouching, transversely in the area 2. Each two successive fields 4 areseparated by an intermediate surface 5, wherein information is coded inthe succession of the fields 4 and the intermediate surfaces 5 ofdifferent widths. At least the fields 4 have diffraction structure whichis embedded in the label 1. The intermediate surfaces 5 are for examplein the form of reflecting or absorbing bars. In another embodiment theintermediate surfaces 5 also have diffraction structures, the azimuth ofwhich differs from the azimuth of the diffraction structure in thefields 4 at least by ±20° modulo 180°. All fields 4 and all intermediatesurfaces 5 respectively are advantageously occupied by the sameoptically effective structure. The label 1 is fixed for example to anarticle 6 and in the bar code 3 contains information about the article6. The article 6 can be a document, a sheet of paper, a sticker or athree-dimensional body and so forth. According to the purpose of use,disposed on the remaining surface area of the label 1 are emblems 7,digits or letters 8 which serve for visual recognition of the origin ofthe label 1. Those items of information can be applied by a printingprocess or however in the form of a diffractive surface pattern which isknown from above-mentioned EP 0 105 099 B1 and EP 0 375 833 B1, thediffraction structures of which are also embedded in the label 1. Inanother embodiment of the label 1 there is also space for an additionalbar code field 9 in which a further bar code produced by a printingprocess or a further diffractive bar code is arranged. The bar codefield 9 is advantageously oriented in parallel relationship with thearea 2 so that the same reading apparatus can machine-read the furtherbar code from the bar code field 9 and the diffractive bar code 3 fromthe area 2.

FIG. 2 shows a view of the label 1 in cross-section. The label 1 is alayer composite 15 which comprises a plurality of layers 10 through 14and which is delimited on the one side by a cover layer 10 and on theother side by an adhesive layer 14. Disposed under the cover layer 10 insuccession in the specified sequence are an embossing layer 11, areflection layer 12, a protective layer 13 and the adhesive layer 14. Atleast the cover layer 10 and the embossing layer 11 are transparent forat least one wavelength of light 17 incident on the label 1.Microscopically fine relief structures 16 are formed in the embossinglayer 11 and diffract the, for example visible, incident light 17. Thereflection layer 12 which is less than 100 nm in thickness covers themicroscopically fine relief structures 16 in such a way as to be true tothe shape thereof. The protective layer 13 fills the recesses of therelief structures 16 and covers the structured reflection layer 12. Theadhesive layer 14 permits a secure join between the article 6 and thelayer composite 15.

Various design configurations of the layer composite 15 and variousforms of the materials suitable for the production thereof aresummarized in Tables 1 through 6 of above-mentioned U.S. Pat. No.4,856,857. Indicia 18 applied by a printing process are disposed atleast on one of the layers 10 through 14 of the layer composite 15, witha light-absorbing ink. In one embodiment the layers 1 areindividualized, or numbered in the sequence of manufacture thereof, by afurther bar code in the bar code field 9 (FIG. 1), the further bar codebeing produced by a printing process on the cover layer 10 in the formof indicia 18.

FIG. 3 shows by way of example a rectangular profile of a flatdiffraction grating in cross-section transversely with respect to thegrooves 19 of the rectangular profile. The grating vector k is thereforein the plane of the drawing. The rectangular profile has a geometricalprofile depth indicated at D. As the light 17 is incident through thecover layer 10 and the embossing layer 11 onto the diffraction gratingformed by the reflection layer 12, the grooves 19 are filled with thematerial of the embossing layer 11. Instead of the geometrical profiledepth D, the optical profile depth d=D•n is operative here, wherein n isthe refractive index of the material of the embossing layer 11. Therectangular profile is shown only for the sake of simplicity instead ofthe diffractive relief structure 16 (diffraction structure) which isdescribed hereinafter.

If the diffraction structure has more than 2,300 lines per millimeterthe light 17 which is incident in perpendicular relationship and in anunpolarized condition, from the visible range of the spectrum, isdiffracted only into the zero order. For the light 17 which is incidentobliquely onto the diffraction structure the line density is to becorrespondingly increased, for example to a value of 2,800 lines permillimeter to 3,000 lines per millimeter. As in the case of a flatmirror the angle between the incident light 17 and the normal onto theplane of the diffraction structure is equal to the angle between thediffracted light and the normal. Such diffraction structures arereferred to hereinafter as zero-order diffraction structures. Uponillumination with white daylight, unlike the flat mirror, the lightdiffracted at the zero-order diffraction structure has gaps in thevisible part of the spectrum so that the zero-order diffractionstructure acts like a mirror which reflects in color.

FIG. 4 shows a graph for the diffraction efficiency E of the flatdiffraction structure for TE and TM polarized light, in dependence onthe optical profile depth d=D, wherein the refractive index n=1. The TEpolarized light is diffracted with a high degree of efficiency Epractically independently of the profile depth D. In contrast theretothe diffraction efficiency E for the TM polarized light is stronglydependent on the profile depth D, wherein the diffraction efficiency Efor the TM polarized light drops rapidly with increasing profile depth Dto a first minimum. When the direction of the light 17 which is incidentin an unpolarized condition and the grating vector k (FIG. 3) of thediffraction structure are in one plane the electrical field vector ofthe p-polarized light oscillates in parallel relationship with thatplane while the electrical field vector of the s-polarized lightoscillates perpendicularly thereto. The diffraction structure used forthe bar code 3 is advantageously of a profile depth T_(G) in theproximity of the first minimum as it is at that location thatpolarization of the diffracted light is at its greatest. The diffractedlight is therefore linearly polarized, that is to say the diffractiverelief structure 16 acts as a polarizer or for the light 17 incident ina polarized condition (FIG. 3) as an analyzer. A useable range of thegeometrical profile depth D includes values T_(G) of between 50 nm and350 nm. As shown in Table 6 in above-mentioned U.S. Pat. No. 4,856,857materials suitable for the embossing layer 11 have a refractive index nin the range of between 1.4 and 1.6.

If the diffraction structure is turned in its plane through 90°, inwhich case now the grooves 19 are parallel and the grating vector kperpendicular to the plane of the drawing in FIG. 3, the light which iss-polarized in relation to the plane of the incident light 17 (FIG. 3)is absorbed and the p-polarized light diffracted as indicated by theefficiency curve TE. The direction of the grating vector k (FIG. 3) canbe established on the basis of the polarization capability of thatdiffraction structure.

The label 1 shown in FIG. 5 is cut out of the layer composite 15 (FIG.2). The microscopically fine optically active structures, that is to saydiffraction structures, mirrors and so forth, which are embedded betweenthe layers 11 and 13 (FIG. 2) of the layer composite 15 and which arecovered with the reflection layer 12 (FIG. 2), define the narrowrectangular fields 4 and the intermediate surfaces 5 of themachine-readable diffractive bar code 3 in the area 2. A firstdiffractive relief structure 16 (FIG. 3) is formed in the embossinglayer 11 in the fields 4. The first diffractive relief structure 16 isan additive superimposition consisting of the first zero-orderdiffraction structure with the first grating vector k1 and amicroscopically fine, light-scattering relief structure. Themicroscopically fine, light-scattering relief structure is a structurefrom the group of isotropically or anisotropically scattering mattstructures, kinoforms or Fourier holograms. The diffractive reliefstructure 16 produced in that way affords the advantage that, incontrast to the flat diffraction structure, the diffracted light isreflected back into the entire half-space over the diffractive reliefstructure 16, independently of the angle of the light 17 incident on thediffractive relief structure 16 (FIG. 3). The light-scattering reliefstructure is advantageously so selected that the diffracted light ispreferably backscattered in a direction towards the reading apparatus.That is a prerequisite for being able to use commercially availablereading apparatuses for bar codes produced by a printing process, forreading the practically forgery-proof bar code 3. If the microscopicallyfine, light-scattering relief structure is a kinoform, the light sourceof the reading apparatus must produce coherent light as otherwise thedesired scatter effect fails to occur.

In another embodiment of the bar code 3 the intermediate surfaces 5 areoccupied by at least one further diffractive diffraction structure withthe further grating vector k2 whose azimuth differs from the azimuth ofthe first grating vector k1 by at least ±20° modulo 180°. In anotherembodiment the intermediate surfaces 5 have a reflective surfacestructure, for example a flat mirror surface or a zero-order diffractionstructure.

In a further embodiment all intermediate surfaces 5 are occupied by asecond diffractive relief structure 20 (FIG. 3). The second diffractiverelief structure 20 is a superimposition consisting of a secondzero-order diffraction structure with the second grating vector k2 andone of the above-mentioned, microscopically fine, light-scatteringrelief structures. The grating vectors k1 and k2 enclose an azimuthangle in the range of between 45° and 135°, wherein the two gratingvectors k1 and k2 are preferably oriented perpendicularly to each other,as illustrated in the drawing in FIG. 5.

In a preferred embodiment the first zero-order diffraction structure andthe second zero-order diffraction structure involve the same parameters,except for the direction of the grating vectors k1 and k2. If the firstrelief structure 16 and the second relief structure 20 differ only inregard to the direction of the grating vectors k1 and k2 of the twozero-order diffraction structures, the bar code 3 cannot be recognizedwithout auxiliary means as, for an observer, both the fields 4 and alsothe intermediate surfaces 5 appear as being equally bright and of thesame color. Auxiliary means are here illumination of the bar code 3 withpolarized light or viewing the bar code 3 through an opticalpolarization filter. When the bar code 3 is viewed through the opticalpolarization filter the observer sees for example the fields 4 in theform of light bars which are separated by intermediate surfaces 5 whichappear as dark bars. After rotation of the polarization filter in itsplane through 90° the fields 4 are the dark bars and the intermediatesurfaces 5 are the light bars.

That embodiment of the bar code 3 has a further advantage: The bar code3 is still readable if a further bar code produced by a printing processis arranged in the area 2 as indicia 18 (FIG. 2) over the diffractivebar code 3. The indicia 18 are bars 21 of the further bar code, whichare separated by color-free intermediate spaces, and are printed on orunder the cover layer 10 of the layer composite 15 (FIG. 2), with alight-absorbing ink. The further bar code produced by a printing processcan also be recognized with the commercially available readingapparatus. The bars 21 and the color-free intermediate spaces disposedtherebetween are oriented in parallel relationship with the fields 4 andintermediate surfaces 5 of the diffractive bar code 3. Only one pair ofthe bars 21 is shown in the drawing of FIG. 5 for illustrative reasons.Recognizability of the narrow bars of the diffractive bar code 3 is acondition for a successful reading operation. The bars 21 of the furtherbar code may cover the narrow bars of the diffractive bar code 3 at mostin a range of between 50% and 70%, that is to say the surfaces of eachfield 4 and of each intermediate surface 5 are at least 30% visiblethrough the color-free intermediate spaces. Each label 1 can beinexpensively individualized with the further bar code, for example butserial numbering thereof.

FIG. 6 shows the area 2 with the first diffractive bar code 3 and thebar code field 9 which is parallel to the area 2, with a seconddiffractive bar code 24 formed from field surfaces 22 and intermediatefields 23. If in an embodiment of the label 1 the area 2 and the barcode field 9 meet with their longitudinal sides the area 2 and the barcode field 9 form a field portion 25 of the label 1. The two diffractivebar codes 3, 24 are arranged in mutually juxtaposed relationship andparallel in the field portion 25. So that the two bar codes 3, 24 arerecognized separately in the machine reading procedure, the fields 4 ofthe first bar code 3 differ from the field surfaces 22 of the second barcode 24 at least by virtue of their polarization capacity. The fields 4have the above-described first diffractive relief structure 16 (FIG. 3).The field surfaces 22 of the second bar code 24 are occupied by theabove-described second diffractive relief structure 20 (FIG. 3). Thefirst and second grating vectors k1 (FIG. 5); k2 (FIG. 5) areadvantageously oriented in mutually perpendicular relationship. Theintermediate surfaces 5 and the intermediate fields 23 have at least onefurther diffractive relief structure with a further grating vector kwhose azimuth differs from the azimuths of the first and second gratingvectors k1; k2 by at least ±20°, or one of the above-mentionedreflective surface structures. In the incident light 17 (FIG. 3) withthe one polarization effect, as viewed from the direction of the lightsource, the fields 4 appear light and the intermediate surfaces 5 andthe second diffractive bar code 24 dark. In the incident light 17 withthe other polarization effect, the field surfaces 22 are light and theintermediate fields 23 and the first diffractive bar code 3 dark.

The above-discussed diffractive bar codes 3, 24 are of a height H in therange of between 0.8 cm and 2 cm. The width B of the narrow bars is atleast 90 μm.

In another embodiment the two bar codes 3, 24 are not arranged inmutually parallel juxtaposed relationship but, as shown in FIGS. 7 a and7 b, they are arranged in the area 2 in such a way that the two barcodes 3 and 24 determine the optically effective structures of first andsecond surface portions 27, 28 of a nested bar code 26, wherein each twoadjacent first surface portions 27 associated with the first bar code 3are separated by one of the second surface portions 28 associated withthe second bar code 24. The surface portions 27, 28 of the nested barcode 26 are of half the area of the bars of the bar codes 3 and 24respectively, which are formed from the fields 4 and the intermediatesurfaces 5 and from the field surfaces 22 and the intermediate fields 23respectively. The nesting effect can be very finely subdivided, in whichrespect the bars, irrespective of their width B (FIG. 6), are brokendown in an integral number of surface portions 27 and 28 respectively asthe surface portions must only involve a minimum width of 15 μm.

In the drawing of FIG. 7 a for example the narrow bars of the bar codes3 and 24 respectively are associated with a surface portion 27 and 28and the wide bars are associated with two surface portions 27 and 28respectively. The equal-sized first surface portions 27 and secondsurface portions 28 are so arranged with their longitudinal sidesalternately in the area 2 that a respective one of the first surfaceportions 27 is followed by one of the second surface portions 28. Theoptically effective structures in the first surface portions 27 and inthe second surface portions 28 are arranged in the sequencepredetermined by the bar code 3 and the bar code 24. In the drawing inFIG. 7 the arrows 29, 30 show how the nested bar code 26 is composed ofthe two bar codes 3 and 24. For the sake of clarity the surface portions27, 28 are hatched to correspond to the association with the bars 4, 5,22, 23. The first surface portions 27 of the fields 4 are longitudinallystriped with respect to the longitudinal extent of the area 2. The firstsurface portions 27 of the intermediate surfaces 5 involve hatchingwhich is inclined towards the right. The second surface portions 28associated with the field surfaces 22 are without hatching whilehatching inclined towards the left marks the second surface portions 28of the intermediate fields 23.

The narrow bars of a width of between about 90 μm and 120 μm aresubdivided a maximum of eight times by the surface portions 27, 28 whichare at least 25 μm wide. The commercially available reading apparatusilluminates the bar code with a light beam optically scanning the area 2lengthwise, in an illuminated spot 31 of a diameter of about 0.1 mm. Theilluminated spot 31 extends over the surface portions 28 and 27respectively which belong to one of the narrow bars.

The above-described nesting of the two bar codes 3, 24 is only one of alarge number of possible options. Another embodiment of the nested barcode 26 as shown in FIG. 7 b has a chessboard-like arrangement ofpixel-like equal-sized surface portions 27, 28 of a side length ofbetween about 15 μm and 25 μm, wherein the first surface portions 27 ofthe first diffractive bar code 3 occupy the place of the black squaresin the chessboard and the second surface portions 28 of the seconddiffractive bar code 24 occupy the place of the white squares.Associated with the surface portions 27, 28 are the optically activestructures in the succession of the bars of the two bar codes 3, 24.

The height H (FIG. 7 a) of the bars of the bar codes 3, 24, 26 is of avalue in the range of between 0.8 cm and 2 cm. That height H at thelimits permits reading of the bar codes 3, 24, 26 discussed herein, in adirection which is oblique in relation to the longitudinal edge of thearea 2, 9 (FIG. 6), 25 (FIG. 6). Hereinafter the area 2, 9, 25 is alsorepresentative in respect of the bar code field 9 and the field portion25.

FIG. 8 diagrammatically shows a reading arrangement having a readingapparatus 32 for the bar codes 3, 24, 26. A light source 33 produces areading beam 34 with polarized or unpolarized light, which is repeatedlyreciprocated over a reading region 35 by the reading apparatus 32 with adeflection device (not shown here). As soon as the area 2, 9, 25 of thelabel 1 on the article 6 comes into the reading region 35, light 36which is backscattered in the illuminated spot 31 (FIG. 7) is modulatedin intensity in accordance with the bar code 3, 24, 26. Thebackscattered light 36 is incident in the reading arrangement 32 on atleast one photodetector 37. The backscattered light 36 is converted bythe photodetector 37 into electrical signals which are proportional tothe intensity of the backscattered light 36 and which are analyzed bythe reading apparatus 32. If the reading apparatus 32 recognizes thelight modulation as that of a bar code known to it, a code numbercorresponding to the information of the bar code 3, 24, 26 is deliveredto a device 38 which provides for further processing of the code number.

If the diffractive bar code has only the one, above-describeddiffractive relief structure 16 acting as a polarizer (FIG. 3), thebackscattered light 36 of the diffractive bar code is readable with theabove-discussed reading apparatus 32 if a first optical polarizationfilter 39 is arranged at least in front of the photodetector 37 and isso oriented that the polarized backscattered light 36 passes the firstpolarization filter 39 in an unattenuated condition. When usingpolarized light for the reading beam 34 the light must be polarized insuch a way that diffraction occurs at the first relief structure 16 atmaximum efficiency. That is the case for example if the reading beam 34and the backscattered light 35 pass through the same polarization filter39 arranged in front of a window 40 of the reading apparatus 32, and thefirst diffractive relief structure 16 is oriented as an analyzer inrespect of azimuth onto the polarization plane of the polarizationfilter 39.

If surfaces with two diffractive relief structures 16 and 20 acting aspolarizers (FIG. 3) are arranged on the label 1 and the diffractiverelief structures 16 and 20 differ at least in respect of thepolarization capacity, then a reading arrangement as shown in FIG. 9 iscapable of separately reading off the items of information contained inthe first and second diffractive relief structures 16 (FIG. 3) and 20(FIG. 3). If an unpolarized reading beam 34 is used, a secondphotodetector 43 is sufficient, which at the same time receives thelight 36 backscattered at the second relief structure 20 acting as apolarizer, wherein a second optical polarization filter 41 is arrangedin front of the second photodetector 43 oriented in such a way that onlythe light 36 backscattered at the second relief structure 20 penetratesto the second photodetector 43.

In a simple embodiment the reading arrangement includes two commerciallyavailable reading apparatuses 32, 42 which are so oriented that thebackscattered light 36 is incident both in the first photodetector 37 inthe first reading apparatus 32 and also in a second photodetector 43 ofthe second reading apparatus 42. The unpolarized light of the readingbeam 34, which is emitted by the light source 33 of the first readingapparatus 32, is scattered at the two diffractive relief structures 16,20 of the diffractive bar code 3 into the half-space over the bar code3. The first polarization filter 39 arranged in front of the firstphotodetector 37 is only transmissive in respect of the light 36backscattered at the first diffractive relief structures 16 while thesecond photodetector 43, behind the polarization filter 41, receivesexclusively the light 36 backscattered by the second diffractive reliefstructures 20. The light source 44 in the second reading apparatus 42 isnot required.

An output 45 of the first photodetector 36 and an output 46 of thesecond photodetector 43 are connected to an analyzer 47 of the readingarrangement. The analyzer 47 produces the code number for the device 38which provides for further processing and which is connected to theanalyzer 47. In the reading operation simultaneously the signalsproduced by the photodetectors 36, 43 are processed and thecorresponding code numbers transmitted to the processing device 38.

The reading arrangement with two commercially available readingapparatuses 32, 42 is suitable for reading off the above-describeddiffractive bar code 3 whose fields 4 (FIG. 5) are occupied by the firstdiffractive relief structure 16, the intermediate surfaces 5 thereof(FIG. 5) being occupied by the second diffractive relief structure 20.Therefore, at any time, at the two outputs 45 and 46, the signalsproduced by the photodetectors 37, 43 in the operation of reading offthat bar code 3 are complementary to each other. That advantageouslypermits checking of the read bar code 3, from the security point ofview.

The bars (21 (FIG. 5) of the further bar code which, as described above,is applied for example to the cover layer 10 by a printing process overthe diffractive bar code 3 produced from the first diffractive reliefstructure 16 and the second diffractive relief structure 20, absorb thelight 36 which is incident in the illuminated spot 31 (FIG. 7). Thenarrow bars 21 are approximately as wide as the diameter of the spot 31illuminated by the reading beam 34 and the wide bars 21 are at leasttwice as wide as the narrow bars 21. The narrow bars of the diffractivebar code 3 are of the width B (FIG. 6) of at least three narrow bars sothat in the color-free intermediate spaces of the further bar code, atleast 30% of the area of the fields 4 and the intermediate surfaces 5respectively is visible. If the spot 31 covers the bar 21, nobackscattered light 36 is produced and no signal from the photodetectors37, 43 occurs at the two outputs 45, 46. Inputs of a logic unit 48 areconnected to the two outputs 45, 46. For the duration of a coincidenceof the state “no signal” on the two outputs 45, 46, the logic unit 48changes its output signal and, on a line 49 between the logic unit 48and the analyzer 47, produces the reading signal for the further barcode formed from the bars 21. The analyzer 47 produces therefrom thecode number corresponding to the individual information of the labels 1(FIG. 1), which is contained in the further bar code which has been readoff. The information of the diffractive bar code 3 which is read out atthe same time with the further bar code gives for example informationabout the issuer of the labels 1. The advantage of that readingarrangement is that it simultaneously reads the further bar codeproduced by printing and the diffractive bar code 3 and is made up fromcommercially available reading units 32, 42.

So that, in the operation of machine reading of the bar codes 3, 24, 26,no faults occur due to light diffracted at the emblems 7 (FIG. 8) anddigits and letters 8 (FIG. 8) formed from diffractive grating structuresarranged mosaic-like, the azimuths of the grating vectors k of thosediffractive grating structures differ by at least ±20° from the azimuthsof the grating vectors k1, k1 and k2 respectively of the diffractionstructures used in the diffractive bar codes 3, 24, 26. If for examplethe grating vectors k1 and k2 involve the azimuths 0° and 90°, then theazimuths of the grating vectors k are to be selected from the ranges ofbetween 20° and 70°, and 110° and 160°, in each case modulo 180°.

Instead of visible light it is also possible to use the adjacent rangesof the spectrum of visually visible light, in particular the nearinfrared range.

As can be seen from FIG. 4 unpolarizedly incident light 17 (FIG. 9) isnot completely linearly polarized at the first and second diffractiverelief structure 16 (FIG. 9) respectively. The backscattered light 36(FIG. 9) has, for each diffractive relief structure 16, besides theintensive component diffracted in accordance with the efficiency curveTE, also a weaker component diffracted in accordance with the efficiencycurve TM. However the intensity of one of the two polarized componentsof the backscattered light 36 predominates in such a way that forexample the one reading apparatus 32 (FIG. 9) receives the moreintensive component through the first polarization filter 39 (FIG. 9)while the weaker component reaches the other reading apparatus 42 (FIG.9) through the second polarization filter 41 (FIG. 9). The readingapparatuses 32, 42 react only to the component of the backscatteredlight 36 involving the higher intensity.

1. A label comprising a layer composite with microscopically fine,optically active structures which are embedded between an embossinglayer and a protective layer of the layer composite and which arecovered with a reflection layer and which in a band-shaped area form atleast one machine-readable diffractive bar code and which are arrangedin the form of narrow rectangular fields with a first diffractive reliefstructure and intermediate surfaces separating the fields, wherein thefirst diffractive relief structure is formed from an additivesuperimposition of a first zero-order diffraction structure with amicroscopically fine, light scattering relief structure, wherein thefirst zero-order diffraction structure has a spatial frequency of morethan 2,300 lines per millimeter, a geometrical depth in the range ofbetween 50 nm and 350 nm and a first grating vector which establishes alinear polarization capacity of the first zero-order diffractionstructure, wherein the microscopically fine, light-scattering reliefstructure is a structure from the group which is formed fromisotropically scattering matt structures, anisotropically scatteringmatt structures, kinoforms and Fourier holograms, so that the firstdiffractive relief structure diffracts and backscatters light into thehalf-space above the first diffractive relief structure, wherein thediffracted and backscattered light is linearly polarized in a planepredetermined by said grating vector, and wherein the microscopicallyfine, optically active structures differ at least with respect to thepolarization capacity from the first diffractive relief structure.
 2. Alabel as set forth in claim 1, wherein a second diffractive bar codeformed from field surfaces and intermediate fields is arranged parallelto the first diffractive bar code in the area, the field surfaces of thesecond bar code have a second diffractive relief structure which is asuperimposition of a second zero-order diffraction structure having asecond grating vector with the microscopically fine, light-scatteringrelief structure, wherein the first grating vector of the firstzero-order diffraction structure and the second grating vector of thesecond zero-order diffraction structure include an azimuth angle in therange of between 45° and 135°, and the intermediate surfaces and theintermediate fields have at least one further diffractive reliefstructure with a further grating vector, wherein the azimuth of thefurther grating vector differs from the azimuth of the first and secondgrating vectors.
 3. A label as set forth in claim 2, wherein the firstand second bar codes are mutually nested, wherein both the fields andthe intermediate surfaces of the first bar code have a predetermineddivision into first surface portions and also the field surfaces and theintermediate fields of the second bar code have the same division intosecond surface portions, in the area in the sequence predetermined bythe two bar codes the first surface portions and the second surfaceportions are arranged in such a way that each two adjacent first surfaceportions are separated by a respective one of the second surfaceportions.
 4. A label as set forth in claim 2, wherein the first andsecond zero-order diffraction structures involve the same parametersexcept for the direction of the first and second grating vectors.
 5. Alabel as set forth in claim 4, wherein the direction of the first andsecond grating vectors and the grating vectors are oriented in mutuallyperpendicular relationship.
 6. A label as set forth in claim 1, whereinat least one of the layers of the layer composite has indicia which areprinted on with light-absorbing ink.
 7. A label as set forth in claim 6,wherein some of the indicia form lines of an optically machine-readableprintable bar code, wherein the lines are separated by color-freeintermediate spaces disposed therebetween and are oriented in parallelrelationship with the fields and the intermediate surfaces of thediffractive bar code.
 8. A label as set forth in claim 1, wherein theintermediate surfaces of the first diffractive bar code have at leastone further diffractive diffraction structure with a further gratingvector, wherein the azimuth of the further grating vector differs fromthe azimuth of the first grating vector.
 9. A label as set forth inclaim 8, wherein the further diffractive diffraction structure in theintermediate surfaces is a further diffractive relief structure, thefurther diffractive relief structure is produced by a superimposition ofa microscopically fine, light-scattering relief structure with a furtherzero-order diffraction structure having a further grating vector, andwherein the further grating vector differs in azimuth from the firstgrating vector by at least ±20° modulo 180°.
 10. A label as set forth inclaim 9, wherein the first and the further zero-order diffractionstructures involve the same parameters except for the direction of thefirst and the further grating vectors.
 11. A label as set forth in claim1, wherein the intermediate surfaces of the diffractive bar code arelight reflective or absorbing bars.
 12. A label as set forth in claim 2,wherein the intermediate surfaces of the diffractive bar code are lightreflective or absorbing bars.
 13. A label as set forth in claim 2,wherein the intermediate fields of the second diffractive bar code havea second further diffraction structure with a second further gratingvector, wherein the azimuth of the second further grating vector differsfrom the azimuth of the further grating vector in the intermediatesurfaces.
 14. A label as set forth in claim 13, wherein second furtherdiffraction structure has the same parameter as the second zero-orderdiffraction structure except for the direction of the further secondgrating vector.
 15. A reading arrangement for optically reading items ofinformation out of an area on a label as set forth in claim 9comprising: a) a first bar code reading apparatus comprising atransparent window, a reading beam issuing through the window foroptically scanning a reading region, a first photodetector which isadapted to receive light of the reading beam which is backscattered inthe reading region, and an optical first polarization filter arranged infront of the first photodetector for filtering out the backscatteredlight which is not linearly polarized in predetermined fashion, b) asecond bar code reading apparatus comprising a transparent window, aninactive light source and a second photodetector, wherein the second barcode reading apparatus is adapted to receive the light backscattered inthe reading region of the reading beam of the first bar code readingapparatus, and wherein a second optical polarization filter is arrangedin front of the second photodetector and oriented in rotatedrelationship through a predetermined angle with respect to the firstoptical polarization filter for filtering out the backscattered lightwhich is not linearly polarized in predetermined fashion, and c) a firstoutput of the first photodetector and a second output of the secondphotodetector, at which appear electrical signals proportional to theintensity of the light backscattered onto the photodetectors, and d) asignal analyzer connected to the first output and to the second outputfor producing a code number for the electrical signals from thephotodetectors transmitted from the first output and from the secondoutput to the signal analyzer and the signals produced by thephotodetectors in the operation of reading off the read bar code arecomplementary to each other allowing a security check of the read barcode.
 16. A reading arrangement for optically reading items ofinformation out of an area on a label as set forth in claim 10comprising: a) a first bar code reading apparatus comprising atransparent window, a reading beam issuing through the window foroptically scanning a reading region, a first photodetector which isadapted to receive light of the reading beam which is backscattered inthe reading region, and an optical first polarization filter arranged infront of the first photodetector for filtering out the backscatteredlight which is not linearly polarized in predetermined fashion, b) asecond bar code reading apparatus comprising a transparent window, aninactive light source and a second photodetector, wherein the second barcode reading apparatus is adapted to receive the light backscattered inthe reading region of the reading beam of the first bar code readingapparatus, and wherein a second optical polarization filter is arrangedin front of the second photodetector and oriented in rotatedrelationship through a predetermined angle with respect to the firstoptical polarization filter for filtering out the backscattered lightwhich is not linearly polarized in predetermined fashion, and c) a firstoutput of the first photodetector and a second output of the secondphotodetector, at which appear electrical signals proportional to theintensity of the light backscattered onto the photodetectors, and d) asignal analyzer connected to the first output and to the second outputfor producing a code number for the electrical signals from thephotodetectors transmitted from the first output and from the secondoutput to the signal analyzer and the signals produced by thephotodetectors in the operation of reading off the read bar code arecomplementary to each other allowing a security check of the read barcode.
 17. A label as set forth in claim 9, wherein at least one of thelayers of the layer composite has indicia which are printed on withlight-absorbing ink and some of the indicia form lines of an opticallymachine-readable printed bar, wherein the lines are separated bycolor-free intermediate spaces disposed there between and are orientedin parallel relationship with the fields and the intermediate surfacesof the first diffractive bar code, wherein the printed bar code isarranged over the first diffractive bar code and at least 30% of eachfield and each intermediate surface of the first diffractive bar code isvisible through the color-free intermediate spaces.
 18. A readingarrangement for optically reading items of information out of an area ona label as set forth in claim 15 comprising: a) a first bar code readingapparatus comprising a transparent window, a reading beam issuingthrough the window for optically scanning a reading region, a firstphotodetector which is adapted to receive the light of the reading beamwhich is backscattered in the reading region; and an optical firstpolarization filter arranged in front of the first photodetector forfiltering out the backscattered light which is not linearly polarized inpredetermined fashion, b) a second bar code reading apparatus comprisinga transparent window, an inactive light source and a secondphotodetector, wherein the second bar code reading apparatus is adaptedto receive the light, backscattered in the reading region, of thereading beam of the first bar code reading apparatus, and a secondoptical polarization filter arranged in front of the secondphotodetector and oriented in rotated relationship through apredetermined angle with respect to the first optical polarizationfilter for filtering out the backscattered light which is not linearlypolarized in predetermined fashion, and c) a first output of the firstphotodetector and a second output of the second photodetector havingelectrical signals proportional to the intensity of the lightbackscattered onto the photodetectors, and d) a signal analyzerconnected to the first output and to the second output for producing acode number for the electrical signals from the photodetectorstransmitted from the first output and from the second output to thesignal analyzer. e) a logical element is connected with one of itsinputs to the output of the first photodetector and with another one ofits inputs to the output of the second photodetector and by means of anoutput line the output of the logical element is connected to the signalanalyzer wherein the logical element produces an output signal for theduration of a coincidence of the state “no signal” on the two outputs ofthe photodetectors, so that the signal analyzer produces a secondreading signal corresponding to the printed bar code.